XMPP isn't an "open federation protocol" it's just a protocol that includes a means to federate; doing so is a matter of server preference. It would be great if more large services federated, but I'd rather have them use XMPP and not federate than build more custom protocols and not use XMPP at all so that I can't write a third party client for them.

My point is that being based on XMPP is still a good thing, regardless of whether they federate or not.